Photonic crystals (also termed photonic bandgap structures) are currently being investigated for electromagnetic (EM) wave applications. Such photonic crystals have a two- or three-dimensional periodic array structure in which the propagation of EM waves is governed by band-structure types of dispersion relationships. These photonic crystals provide electromagnetic analogs to electron-wave behavior in crystals, with electron-wave concepts such as reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, van Hove singularities and tunneling having electromagnetic counterparts in photonic crystals. This will enable the development of many new and improved types of photonic crystal devices, including devices in which optical modes, spontaneous emission, and zero-point fluctuations are greatly reduced or inhibited. Photonic crystals may also be formed with local disturbances in the periodic array structure, thereby generating defect or cavity modes with frequencies within a forbidden bandgap of the crystal for forming additional types of photonic crystal devices, including high-Q resonators and filters.
The photonic crystals formed heretofore have generally been formed by machining processes whereby material is removed from a substrate or the like for forming the crystals. These machining processes, using conventional machine tools (e.g. mechanical drills and mills) or laser ablative machining, have been used for forming photonic crystals having bandgaps at microwave or millimeter-wave frequencies. Material removal from a substrate by etching or ion milling has also been proposed for forming photonic crystals.
An advantage of the method of the present invention is that photonic crystal devices may be formed by a selective growth process using irradiation with a charged-particle beam such as an electron beam or an ion beam, with a plurality of spaced elements therein being located with a very high precision (down to a few nanometers).
Another advantage of the present invention is that use of charged-particle-beam assisted growth of one or more photonic crystal devices upon a substrate allows the devices to be formed at predetermined locations on the substrate and with a predetermined periodicity.
Another advantage of the present invention is that a plurality of spaced elements may be simultaneously formed on or above a surface of a substrate by the use of charged-particle-beam assisted deposition, with different elements having the same or different dimensions, spacings, or compositions.
These and other advantages of the photonic crystal device and method of the present invention with become evident to those skilled in the art.